CMSB was first synthesized in 1959 by Campbell and McDonald, reported in J. Org. Chem. 24,1246 (1959). The following references relate to certain uses and syntheses of CMSB: German Pat. No. 1,108,219; German Pat. No. 1,129,947; German Pat. No. 1,134,064; British Pat. No. 913,735; British Pat. No. 924,762; U.S. Pat. No. 3,076,020; U.S. Pat. No. 3,177,208. None of the references disclosed suggests our novel process for the manufacture of CMSB.
Although the cited references indicate that CMSB can be prepared by various routes, for commercial production a process is desirable which is simple, gives a high yield of product and uses commercially available starting materials. The following process meets these criteria: The reaction of alpha,alpha'-dihalo-p-xylene with two moles of triphenyl phosphine gives p-xylylene-bis-(triphenyl-phosphonium halide) in nearly quantitative yield. This compound is converted to a Wittig reagent with a strong base, for example sodium methoxide or another alkoxide, in the presence of 4-carbomethoxybenzaldehyde. The Wittig reagent immediately reacts with two moles of 4-carbomethoxybenzaldehyde to give CMSB. The process scheme becomes practicable due to the fact that 4-carbomethoxybenzaldehyde, or by other name methyl 4-formyl benzoate (MFB), is a by-product of dimethyl terephthalate synthesis and is available on a commercial scale. Although the purity of this commercial by-product is low and the impurities are difficult to remove, we have found that the purity can be increased to a level wherein the impurities become innocuous. The impurities are dimethyl terephthalate and methyl benzoate, and neither of them interferes in the desired reaction of MFB.
The first step of the synthetic scheme, the reaction of alpha,alpha'-dichloro-p-xylene with triphenyl phosphine has been described in the literature using dimethyl formamide solvent. We have found that the reaction can be carried out without a solvent, in the melt, at 100.degree.-200.degree. C., for 0.5 to 5 hours.
According to our novel process for the manufacture of 1,4-bis-[2-(4'-carbomethoxystyrenyl)]-benzene, we react, at a temperature of about 0.degree. C. to about 100.degree. C., in a highly polar, anhydrous organic solvent or solvent mixture, or in liquid ammonia, a p-xylene-bis-(trialkylphosphonium halide) or p-xylylene-bis-(triarylphosphonium halide) with 4-carbomethoxybenzaldehyde initiated by the slow introduction of an organo metallic compound or an inorganic base. The molar ratio of p-xylylene-bis-(trialkylphosphonium halide) or p-xylylene-bis-(triarylphosphonium halide), the 4-carbomethoxybenzaldehyde and the organo metallic compound, or an inorganic base, ranges from about 1.0:2.0:2.0 to about 1.0:2.2:2.8. Useful p-xylylene, bis-trialkyl or triaryl phosphonium halides include: trimethyl phosphonium halides, triethyl phosphonium halides, tripropyl phosphonium halides, tributyl phosphonium halides, triphenyl phosphonium halides, tribiphenyl phosphonium halides and etc. Useful organic phosphonium halides are the chlorides, bromides, and iodides. Solvents useful in our process are toluene, ethanol, methanol, diethyl ether, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, xylene, benzene, and mixtures of these or liquid ammonia and etc. Useful organo metallic compounds include: phenyl lithium, butyl lithium, sodamide, potassium amide, sodium methoxide, sodium ethoxide, potassium ethoxide, sodium carbonate, and potassium carbonate. Useful inorganic bases include sodium hydroxide, ammonium hydroxide and etc.
In a preferred embodiment of our novel process for the manufacture of CMSB, p-xylylene-bis-(triphenylphosphonium chloride) and methyl-4-formyl benzoate (MFB) are dissolved in a suitable solvent, such as pure, dry dimethylsulfoxide, dimethylformamide, or mixture of an aromatic solvent (benzene, toluene, xylenes, etc.) with aliphatic alcohols (absolute methanol, absolute ethanol, etc.). The resulting mixture is stirred extensively and slowly, a solution of an alkali metal alkoxide, such as methanolic sodium methoxide, is introduced dropwise. Conveniently, the reaction temperature can be ambient, or between 0.degree. C. and the reflux temperature of the solvent. The reagents are used in almost stoichiometric quantities. The reaction is almost quantitative. Isolated yields of CMSB (by crystallization) are above 80%; higher isolated yields can be obtained with the use of pure reagents (e.g., using pure MFB and not a commercial source of MFB).
The CMSB obtained in this synthesis is a mixture of cis-cis, cis-trans and trans-trans isomers. The individual geometrical isomers need not be separated. However, for identification purposes, we have separated all the isomers by recrystallization procedures and identified them by their melting points. IR spectra, .sup.1 H NMR spectra, .sup.13 C NMR spectra and mass spectra.
The isomeric mixture of CMSB, as well as the individual isomers, can be hydrolized to the diacid. This, in turn, can easily be converted to the diacid dichloride with thionyl chloride. This latter compound can serve as a monomer or co-monomer for the synthesis of fluorescent polyamides.
CMSB is particularly useful as an optical brightener for polyesters, polyamides and other polymers, including natural products, such as cotton. The optical brightening effect is shown in the tables. The individual geometrical isomers of CMSB, and an isomeric mixture of CMSB, were copolymerized into polyethyleneterephthalate (hereinafter PET) at 20 parts per million level. Higher levels are not useful since the polyester polymer loses the optical qualities, however, at least three parts per million of CMSB are needed. The characterizations, the color measurements and the UV degradation studies of these polymers are summarized in Tables I and II, respectively.
As Table I indicates, the physical and chemical properties of the polymers (inherent viscosity, carboxyl content, diethylene glycol content) were essentially identical, without and with incorporation of CMSB, and were not dependent on the geometrical isomer of the CMSB used.
However, the fluorescence spectra of the polyethyleneterephthalates made with CMSB were quite different than those of the blank PET containing no CMSB. The excitation maxima and emission maxima of the brightened polyesters were at the same wavelength and not dependent on the geometrical isomer of CMSB used. The location of the excitation maxima, 407 nm, measured by reflectance on the solid polymer, differed from that of the CMSB isomers (375 nm) measured in CH.sub.2 Cl.sub.2 solutions. The differences may arise either from the phase of the fluorescing materials or, alternatively, from the chemical changes. The fluorescence intensities of the brightened polyesters differed with the CMSB isomer used in the synthesis. In the case of CMSB monomers, the trans-trans isomer had the highest fluorescence intensity and the cis-cis isomer had the lowest.
Table II summarizes the results of the instrumental color measurements. The L value of the tristimulus color measures the greyness (100=white; 0=black); the a value the red-green hue (red is +; green is -); and the b value the yellow-blue hue (yellow is +; blue is -). The measurements taken on the Diano instrument--which filters out the UV light and hence eliminates the fluorescence--give practically identical color values for the blank and the brightened polymers. The results indicate that the individual geometrical isomers of CMSB gave almost the same color improvement. The color improvements are noticeable even to the naked eye. The b values of Table II show that the incorporation of 20 ppm CMSB into polyethylene terephthalate overcompensates for the yellowness, and the polymer becomes bluish. Probably 3 to 15 ppm CMSB would suffice to compensate for the yellowness and would provide the whitest appearance to the polymer. It is interesting that, while CMSB itself is a yellow compound, its incorporation at trace levels into polyethylene terephthalate removes the yellowness from the polymer by fluorescence.
In the polyesters of Table I, the 20 ppm CMSB has been chemically incorporated into the polymer. Incorporating more than 20 ppm CMSB is detrimental, as is incorporating less than 3 ppm. To support our conclusions concerning the copolymerization of CMSB, the following experiments were carried out: The polymers of Table I were extracted with refluxing toluene in a Soxhlet apparatus to see whether the CMSB can be "extracted out" of the polyethyleneterephthalate. If it were selectively extractable, this would indicate that the CMSB was not chemically incorporated into the polymer. On the other hand, if it were not extractable, the results still would not conclusively prove that it is incorporated because the trans-trans isomer of CMSB is known to be extremely insoluble in solvents which do not attack polyethyleneterephthalate.
Toluene did not attack the polyethyleneterephthalate. The extraction did not result in a weight loss of polyethyleneterephthalate. On the contrary, a 4 to 5 percent weight increase was measured after vacuum drying at 70.degree. C. Apparently, the polyesters adsorbed some toluene. The extracted polyesters became opaque, while originally they were transparent. Table III compares the tristimulus color values of the original with those of the extracted polyesters. The results clearly indicate that the brightener was not removed from the samples.
Table III illustrates that CMSB is incorporated into PET as a copolymer. On the basis of our evaluations, we believe that it is critical to incorporate 3 to 20 ppm of CMSB into commercial PET to compensate for the yellowness of the polymer. Outside this range, CMSB loses its ability to remove the yellow color from the polymers. This level of incorporation is much lower than currently used in polyester fibers. Thus, CMSB is a very outstanding brightener for polyesters. The outstanding brightening effect may be associated with the fact that the excitation maxima of the brightened polyesters is probably at an optimal wavelength (407 nm, see Table I), just at the end of the visible range. Natural light has this wavelength in fairly high intensity, thus providing strong excitation for the fluorescence. Also, the emission maximum of the brightened polyesters is at the right wavelength (443 nm, see Table I), which means emission of blue light. The fluorescence intensities are high.
CMSB is also useful to brighten polyamide and polyimide polymers and other synthetic and natural polymers, such as polymethylmethacrylate, cotton, linen, viscose, etc.
The following examples illustrate the preferred embodiment of this invention. It will be understood that these examples are for illustration purposes only and do not purport to be wholly definitive with respect to the conditions or scope of this invention.